Variable Speed is a miraculous technology that was NOT developed to fix duct problems. ~Chris Lenhard, owner trainer
Why you should get a variable speed motor.
What variable speed technoloy does is electronically control the speed of fan motor to deliver any pre-programmed amount of air. This is important because the efficiency of your system depends on the right amount of air flow and because it can adapt to changing conditions like a dirty air filter, you always get the maximum efficiency and comfort from your system.
Variable Speed motors have selectable humidly profiles that direct the motor ramp up to full speed over several minutes. This greatly enhances the air conditioners ability to remove moisture from the air and creating a environment in you home with really low and comfortable relative humidity.
The motor slowly ramps up to full speed as opposed to BANG -100% full power the way a standard motor operates. It’s so subtle that you will be hard pressed to ever notice it running.
Variable Speed motors are highly efficient motors. Compared to the standard motor that is most likely in your furnace today, the VS is more than 200% more efficient when the motor is run in the continuous mode. Continuous fan operation is a important factor to consistent air temperature throughout the home, clean and properly humidified air.
Its not going to solve your air flow problem on the second floor.
The one thing it can’t do is fix the duct because it’s designed to operate at a static pressure of . (point) 5. Stick with me I am gong to make this easy. Suppose you have a 1 inch diameter inch garden hose and your getting 8 gallons of water per minute at a .5 If you changed the garden hose to a ½ inch diameter would you expect the same gallons per minute? Probably not. If you increased the pressure to a . 9 maybe that would be enough to get 8 gallons but its almost double the pressure which is a lot more work
Duct work behaves the same as a hose but instead of water it’s air. The smaller the duct, the harder the fan has to work to deliver the desired amount of air. The difference between your old motor and these new variable speed motors is the more pressure you put on the old motor the less it actually tries to work. Weird but true. These new variable speed motors are different in that they will commit suicide trying to deliver the desired air at any static they encounter.
I asked the manufacture directly, “ why don’t these motors have a governor in them?” A governor is a speed limiting device that prevents motors, usually combustion motors, from killing them selves. He said they do have one installed then went on to explain this: “ Your car has a governor init that prevents damage to the engine and transmission should you decide to drive to work in first gear. You will actually make it there and probably home. Do it again tomorrow, the next day and so on. Eventually you’re going to fry the governor and then the motor / transmission”
This is what we do we install the Variable Speed motors on duct systems that are too small to handle
them. We fry the governor then fry the motor. Takes about 18 months.
What you should do.
Our sales engineer can determine what the static is going to be before you make the decision. Not everybody has a problem so this may be a non-issue for you but at least you will know going in. If it is abnormally high then either fix the duct or stick with the old style motors. If you decide to fix the duct and get the motor, you won’t ever regret it.